1. Field of the Invention
The present invention relates to a method of manufacturing semiconductor devices, to the apparatus for carrying out the method, and to the resulting device.
2. Brief Description of the Prior Art
One of the currently widely used plastic packages for two-lead semiconductor devices, such as diodes-particularly rectifiers (currents of up to about 1 A and reverse voltages of about 100 V to 2 kV)-, varistors or thermistors, has the shape of a cylinder with leads projecting in the same axis. The semiconductor die or chip and the inner ends of its leads are hermetically embedded in the plastic, e.g., a thermoplastic or a thermosetting plastic, and thus protected against physical damage and chemical influences, such as the entrance of moisture.
In the fabrication of such semiconductor devices with a plastic package, the manufacture of the die starts with a semiconductor wafer on which several 100 to several 1000 identical dies or chips are fabricated, and the leads for the semiconductor device are designed as plug leads ("head leads"), i.e., leads having a thickened, (e.g., upset) portion at one end, referred to as the "head". Between the two heads, the die is attached by soldering, for example.
To achieve a high throughput, a large number of untinned plug leads is fed into magazines, a die, i.e., a semiconductor chip, is positioned on each of the heads, and the heads of other plug leads fed into a further magazine are placed on the dies. In a furnace, each of the dies is then connected with its two associated plug leads by soldering. If the finished semiconductor device is to have a high reverse voltage, the soldered dies are etched and covered with a suitable plastic.
Next, the semiconductor devices are transferred into molds where they are embedded in plastic. Only then are the leads of the individual semiconductor devices tinned, which is done by barrel tinning to achieve a high through-put. Then, however, the leads, which are bent during the tinning process, must be axially aligned again in suitable straightening devices. Only then are they tested, taped, and lettered.
Conventional straightening devices have an hourly through-put of about 20,000 semiconductor devices. As the prices of semiconductor devices are still falling, this through-put rate is much too low if low-cost volume production is to be achieved.
Although the manufacturing process described is a well-proved high-volume process, efforts are being made to modify it, particularly with a view to further reducing the manufacturing costs, and to provide semiconductor devices which can be made at even lower cost.